How many dried mushrooms would I have to eat to die from an overdose of psilocybin?

Using the data for rats and accepting a median of 1% potency, it would require the consumption of 1680g of mushrooms to reach the LD50 for a 60kg "rat".

The LD50 stands for the Lethal Dose that is requied to kill half of an exposed population to a particulare agent or drug.

The LD50 for Psilocybin: From the Merck Index 12th Edition

LD50 285 mg/kg i.v.(mice)

LD50 280 mg/kg i.v. (rats)

LD50 12.5 mg/kg i.v.(rabbits)

We most often extrapolate,
from rats to humans. So let's stick with convention and use the rat
data to compute how many grams of dried mushrooms would be necessary to
reach an overdosage of psilocybin.

Psilocybin content in dry mushrooms varies from species to species and ranges from .2 - 2.37%, 2.37 being the highest reported.

Lets take 1% as the median for "average" percentage and use the 280mg/kg i.v. as the LD50.

We must keep in our minds the LD50
considers intravenous dosage and not oral dosages, and that it's done
on rats and not humans. Though rats are most often the animal models
for humans.

Our question then is, how many mushrooms would one need to eat, if one weighed 60kg to reach the LD50.

Since the dosage is listed as mg/kg, we must multiply our body weight in kg by the LD50.

280mg/kg x 60kg = 16800mg (or 16.8g) of
psilocybin. The units of kg cancel by simple math properties and we're
left with an amount of pure psilocybin that would be required to kill a
"rat" that weighs 60kg.

Since we know the amount of pure psilocybin
that it would take to kill a 60kg "rat" and we have a range of
psilocybin content present in dried mushrooms, we can now figure out a
total dried weight of mushrooms that would be required to reach the LD50.

Thus we've determined that using the data for rats and accepting a median of 1% potency, that it would require the consumption of 1680g of mushrooms to reach the LD50 for a 60kg rat. This amount of mushrooms is enough to provide a "normal" mushroom trip to roughly 650 people.

Some things to keep in mind: Not all data can
be extrapolated from rats to humans, but this common practice and
generally accepted. Note that the LD50
incorporates route of administration. Therefore our answer of 1680g of
mushrooms or 1.68kg of mushrooms is likely an underestimation of the
oral dose required to kill a 60kg rat.